class Compiler {
  constructor(vm) {
    this.el = vm.$el
    this.vm = vm
    this.compile(this.el)
  }

  //编译模板，处理文本节点或元素节点
  compile (el) {
    let childNodes = el.childNodes
    Array.from(childNodes).forEach(node => {

      if (this.isTextNode(node)) {
        //处理文本节点      
        this.compileText(node)
      } else if (this.isElementNode(node)) {
        //处理元素节点
        this.compileElement(node)
      }

      //判断node节点 是否还有子节点，如果有子节点，则递归调用compile
      if (node.childNodes && node.childNodes.length) {
        this.compile(node)
      }
    })
  }

  //编译元素节点，处理指令
  compileElement (node) {
    //遍历所有的属性节点
    Array.from(node.attributes).forEach(attr => {
      //判断是否是指令
      let attrName = attr.name;
      if (this.iSDirective(attrName)) {
        // v-text > text
        attrName = attrName.substr(2)
        let key = attr.value
        this.update(node, key, attrName)
      }
    })
  }

  update (node, key, attrName) {
    let updateFn = this[attrName + 'Updater']
    updateFn && updateFn.call(this, node, this.vm[key], key)
  }

  //处理 v-text 指令
  textUpdater (node, value, key) {
    node.textContent = value;
    new Watcher(this.vm, key, (newValue) => {
      node.textContent = newValue
    })
  }

  //处理 v-model 指令
  modelUpdater (node, value, key) {
    node.value = value;
    new Watcher(this.vm, key, (newValue) => {
      node.value = newValue
    })

    //双向绑定
    node.addEventListener('input', () => {
      // <input type="text" v-model="msg"></input>
      this.vm[key] = node.value
    })
  }

  //编译文本节点，处理差值表达式
  compileText (node) {
    // {{ msg }}
    let reg = /\{\{(.+?)\}\}/
    let value = node.textContent
    if (reg.test(value)) {
      let key = RegExp.$1.trim();
      node.textContent = value.replace(reg, this.vm[key])

      //当前数据改变的时候更新视图-> 创建watcher对象
      new Watcher(this.vm, key, (newValue) => {
        node.textContent = newValue
      })
    }
  }

  //判断元素属性是否是指令
  iSDirective (attrName) {
    return attrName.startsWith('v-')
  }

  //判断节点是否是文本节点
  isTextNode (node) { return node.nodeType === 3 }

  //判断节点是否是元素节点
  isElementNode (node) { return node.nodeType === 1 }
}